add 1137

fishercoder1534 · fishercoder1534 · commit 909762f6bd0e · 2019-08-13T13:34:35.000-07:00
diff --git a/README.md b/README.md
@@ -29,6 +29,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |-----|----------------|---------------|---------------|---------------|--------|-------------|-------------
 |5087|[Letter Tile Possibilities](https://leetcode.com/problems/letter-tile-possibilities/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_5087.java) | O(1) | O(1) | |Medium||
 |5083|[Occurrences After Bigram](https://leetcode.com/problems/occurrences-after-bigram/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_5083.java) | O(n) | O(1) | |Easy||
+|1137|[N-th Tribonacci Number](https://leetcode.com/problems/n-th-tribonacci-number/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1137.java) | O(n) | O(n) | |Easy||
 |1122|[Relative Sort Array](https://leetcode.com/problems/relative-sort-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1122.java) | O(n) | O(n) | |Easy||
 |1071|[Greatest Common Divisor of Strings](https://leetcode.com/problems/greatest-common-divisor-of-strings/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1071.java) | O(m*n) | O(1) | |Easy||
 |1065|[Index Pairs of a String](https://leetcode.com/problems/index-pairs-of-a-string/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1065.java) | O(nlogn) | O(1) | |Medium||
diff --git a/src/main/java/com/fishercoder/solutions/_1137.java b/src/main/java/com/fishercoder/solutions/_1137.java
@@ -0,0 +1,44 @@
+package com.fishercoder.solutions;
+
+/**
+ * 1137. N-th Tribonacci Number
+ *
+ * The Tribonacci sequence Tn is defined as follows:
+ *
+ * T0 = 0, T1 = 1, T2 = 1, and Tn+3 = Tn + Tn+1 + Tn+2 for n >= 0.
+ *
+ * Given n, return the value of Tn.
+ *
+ * Example 1:
+ * Input: n = 4
+ * Output: 4
+ *
+ * Explanation:
+ * T_3 = 0 + 1 + 1 = 2
+ * T_4 = 1 + 1 + 2 = 4
+ *
+ * Example 2:
+ * Input: n = 25
+ * Output: 1389537
+ *
+ * Constraints:
+ * 0 <= n <= 37
+ * The answer is guaranteed to fit within a 32-bit integer, ie. answer <= 2^31 - 1.
+ * */
+public class _1137 {
+    public static class Solution1 {
+        public int tribonacci(int n) {
+            if (n <= 1) {
+                return n;
+            }
+            int[] numbers = new int[n + 1];
+            numbers[0] = 0;
+            numbers[1] = 1;
+            numbers[2] = 1;
+            for (int i = 3; i <= n; i++) {
+                numbers[i] = numbers[i - 1] + numbers[i - 2] + numbers[i - 3];
+            }
+            return numbers[n];
+        }
+    }
+}
diff --git a/src/test/java/com/fishercoder/_1137Test.java b/src/test/java/com/fishercoder/_1137Test.java
@@ -0,0 +1,41 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._1137;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _1137Test {
+    private static _1137.Solution1 solution1;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _1137.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals(2, solution1.tribonacci(3));
+    }
+
+    @Test
+    public void test2() {
+        assertEquals(4, solution1.tribonacci(4));
+    }
+
+    @Test
+    public void test3() {
+        assertEquals(1389537, solution1.tribonacci(25));
+    }
+
+    @Test
+    public void test4() {
+        assertEquals(0, solution1.tribonacci(0));
+    }
+
+    @Test
+    public void test5() {
+        assertEquals(1, solution1.tribonacci(2));
+    }
+}
